Johannes Rydberg

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SWEDISH MATHEMATICIAN AND PHYSICIST
1854–1919

Johannes Robert Rydberg was born in Halmstad, Sweden, on November 8, 1854. His father, Sven, was a local merchant and minor shipowner who died when Rydberg was young. Rydberg attended the local gymnasium (or high school) in Halmstad and studied languages, religion and philosophy, history and geography, and natural history, along with mathematics and physics. Although a good all-around student, Rydberg chose to pursue mathematics at the university.

He entered the University of Lund in the autumn of 1873, and it is fair to say that he never left. He received his doctorate in mathematics from that institute in 1879 and was appointed a teacher of mathematics there in 1881. But in 1876 Rydberg was also appointed as a teaching assistant at Lund's physics institute. His experimental study on friction electricity led to a position as a teacher of physics in 1882.

As a physicist and mathematician, Rydberg was driven by a desire to understand the basic physical laws behind the Periodic Table. He set out to find order in the mass of spectroscopic data that was then available. Atomic spectra had been used to characterize minerals and to ascertain the chemical composition of distant stars, but the underlying order was not apparent. While various spectroscopists had noted that line spectra could be discriminated into "sharp," "principal," and "diffuse" patterns, a guiding relationship between the lines had not yet emerged.

Rydberg decided to use the wave number as a measure of frequency in his calculations. A wave number is the reciprocal of the wavelength, and, although Rydberg did not know this at the time, it is directly related to energy, unlike the more common wavelength that bears an inverse relationship. Having made this change, patterns began to emerge in the data with a particular series of lines for any atom leading to a hyperbolic relationship . Indeed, the same relationship was observed for all the different spectroscopic series and for different elements.

Rydberg devised the formula

n = n ₀ − N ₀ /( m + m ′) ²

and was testing it against the data when the Swiss mathematician and physicist Johann Balmer published his result for hydrogen atoms, wavelength = hm ² /( m ² − 4). Rydberg quickly realized that this was just a special case of his formula with m ′ = 0 and N ₀ = 4 n ₀ and that N ₀ must be a universal constant. Using this information, Rydberg was able to show that his equation was more general and published it in 1890, well before the spectroscopic series discovered by Balmer, the American Theodore Lyman, or the German Friedrich Paschen provided experimental confirmation.

The formula is now written as

1/λ = R _H (1/n ₁ ² − 1/n ₂ ² )

where both values of n are integers, but n ₂ n ₁ . The term N ₀ has been replaced by R _H , the so-called Rydberg constant. It is a fundamental constant of nature and a measure of the strength of the nuclear -electron interaction in atoms.

SEE ALSO Balmer, Johann Jakob ; Spectroscopy .

Todd W. Whitcombe

Bibliography

Bohr, Niels (1954). "Rydberg's Discovery of the Spectral Laws." Proceedings of the Rydberg Centennial Conference on Atomic Spectroscopy, Acta Universitatis lundensis 50: 15–21.

Pauli, Wolfgang (1954). "Rydberg and the Periodic System of the Elements." Proceedings of the Rydberg Centennial Conference on Atomic Spectroscopy, Acta Universitatis lundensis 50: 22–26.

Internet Resources

O'Connor, J. J., and Robertson, E. F. "Johannes Robert Rydberg." Available from http://www-gap.dcs.st-and.ac.uk/,history/Mathematicians/Rydberg.html .